In recent years, a circuit board, and various apparatuses employing the circuit board such as an image forming apparatus, a thermal head, and an image sensor have come to be increasingly smaller.
In order to achieve miniaturization of such apparatuses, a device to be formed on a substrate constituting the circuit board has to be downsized in itself by necessity, in consequence whereof there results a trend toward smaller and smaller conductors. Correspondingly, a diameter of a wire and a size of a bonding tool (such as a capillary) need to be reduced, which has created a demand for enhancement of the strength of adhesion between a conductor and a wire.